Research and Statistics: Number Needed to Treat and Intention to Treat Analysis

Megan M. Tschudy, MD* 2. Peter C. Rowe, MD† 1. *General Academic Pediatrics Fellow, Johns Hopkins University School of Medicine, Baltimore, Md. 2. †Professor of Pediatrics, Division of General and Adolescent Medicine, Johns Hopkins University School of Medicine, Baltimore, Md. An 8-month-old boy who has no history of wheezing or atopy presents to the emergency department with bronchiolitis. While discussing the case, a colleague mentions that a recent randomized, controlled trial in the New England Journal of Medicine (NEJM) showed that the combination of nebulized epinephrine and oral dexamethasone may reduce hospital admissions in children who have bronchiolitis. (1) You have been seeing many patients this season who have bronchiolitis and wonder if you should change your clinical practice. Randomized, controlled trials (RCTs) are considered the gold standard for establishing the beneficial and harmful effects of a treatment. Investigators report the results of treatment using absolute difference in risk (absolute risk reduction), relative risk, or relative risk reduction. (2) Absolute risk reduction is the difference in risk of an event occurring in exposed individuals compared with nonexposed individuals. Relative risk is the ratio of the risk of the event occurring in the exposed population compared with the risk in the nonexposed group. Relative risk reduction is the percent reduction in events occurring in exposed compared with unexposed individuals. These estimates of risk are not easily extrapolated or relevant to clinical practice. Number needed to treat (NNT) analysis is an important measure to …